Digestion in the pig between 7 and 3 d of age. 3. The digestion of nitrogen in pigs given milk and soya-bean proteins.

1. In two separate experiments, forty-four pigs weaned at 4--5 d of age were fed on diets containing milk or soya-bean protein until slaughtered at 14, 28 or 35 d of age. 2. Daily amounts of nitrogen flowing through the stomach and proximal small intestine of pigs were similar with both sources of protein fed. 3. Endogenous N flows in the duodenum, jejunum and ileum of pigs given an N-free diet were 22 . 9, 7 . 4 and 4 . 6 g N/kg dry matter (DM) intake. Endogenous N in faeces was 0 . 970 g N/kg DM intake. 4. The apparent and true digestibility of N to the ileum of 28-d-old pigs was 0 . 86 and 0 . 92 for the pigs given the milk-protein diets, 0 . 80 and 0 . 86 for the pigs given the isolated soya-bean protein (ISP; Promine D) diets and 0 . 51 and 0 . 62 for pigs given the soya-bean meal (SBM)-protein diet. These values over the entire gastro-intestinal tract were 0 . 98 and 1 . 00 for milk, 0 . 92 and 0 . 95 for ISP and 0 . 82 and 0 . 85 for SBM. 5. The apparent and true digestibility of N to the ileum of 14-d-old pigs given a liquid milk diet was 0 . 92 and 0 . 94, while the values for the pigs given a pelleted milk diet were 0 . 86 and 0 . 87. At 35 d of age there were no differences in the apparent digestibility of the N in the liquid an pelleted milk diets. 6. The apparent digestibility of N to the ileum and over the entire gastro-intestinal tract of pigs given ISP (Supro 610) increased with increasing age of pigs from 0 . 83 at 14 d of age to 0 . 88 at 35 d of age. 7. Of the N in the stomach 14--32% could not be precipitated by trichloroacetic acid (TCA; 30 milligram). 8. In the jejunal and ileal contents an average of 46 and 24% of the N was precipitated by TCA in pigs given soya-bean proteins and milk proteins respectively.